Magnetic compositions that are semiflexible or rubbery in nature are used in a wide variety of applications. For instance, such materials are widely used as a combination airtight gasket and magnetic closure for refrigerator and freezer doors. They are also used in decorative magnets that will stick to a wide variety of metal (steel) objects. In any case, such semiflexible or rubbery magnets are typically comprised of a blend of a rubbery polymer and a magnetic powder which is formed into the desired shape and then cured. Such rubbery magnetic compositions also typically lack heat, ultraviolet light and outdoor weather resistance.
Heat and light stabilizers can be employed to improve the heat and ultraviolet light aging characteristics of conventional blends of rubber with magnetic powder. However, the degree to which the aging characteristics of such blends can be improved by the addition of additives is limited. In fact, there is a demand for performance characteristics in such applications which heretofore has not been realized by the utilization of heat and light stabilizers. For instance, it would be highly desirable for rubbery magnets used in refrigerator and freezer doors to have a higher level of resistance to discoloration and cracking under conditions of heat and exposure to ultraviolet light experienced throughout the life of the refrigerator or freezer. Resistance to ultraviolet light is particularly important in out door applications, such as automotive seals and seals for metal framed doors and windows.
U.S. Pat. No. 5,674,933 and U.S. Pat. No. 5,767,173 disclose a rubbery polymer which can be blended with polyvinyl chloride to make leathery compositions having good heat and ultraviolet light resistance, said rubbery polymer being comprised of repeat units which are comprised of (a) butyl acrylate, or optionally a mixture of butyl acrylate and 2-ethylhexyl acrylate containing up to about 40 percent 2-ethylhexyl acrylate, (b) at least one member selected from the group consisting of methyl methacrylate, ethyl methacrylate, methyl acrylate and ethyl acrylate, (c) acrylonitrile, (d) styrene, (e) a surfactant selected from the group consisting of sulfonates and sulfate derivatives, (f) a dispersant selected from the group consisting of aromatic formaldehyde condensation products and polycarboxylates and (g) a crosslinking agent. U.S. Pat. No. 5,380,785 discloses a similar type of rubbery polymer and U.S. Pat. No. 5,616,651 discloses a technique for making a low odor version of the rubbery polymer by adding an aminoalcohol to the emulsion thereof.